Electrohydraulic valve control systems for vehicles and like applications often require differing control modes at various stages of operation. For example, an excavator may require position control of the bucket teeth during a digging cycle, velocity control during other modes of operation, and incremental position control, i.e. position control from a starting or base position, during the fine control cycle. It is conventional to provide separate position and velocity sensors for closed loop feedback during the position and valocity control modes respectively. However, provision of multiple sensors adds to the overall cost and complexity of the system.
It is a general object of the present invention to provide an electrohydraulic valve control system which may selectively operate in either the position or the velocity control mode while employing only one feedback sensor. In this connection, it has been recognized that position feedback is more readily amenable to operator display and automation. It is therfore a more specific object of the invention to provide an electrohydraulic valve control system which employs a position sensor and feedback loop, and which is adapted selectively and alternately to function in either a position control mode or a velocity control mode.
Another object of the invention is to provide an electrohydraulic valve control system of the described character in which position control may be selectively and alternately implemented in either an absolute position control mode or an incremental position control mode, employing the same sensor, preferably a position sensor and feedback loop.